I'm a grandma!

Well not technically but one of my fishies had babies this weekend! She was pregnant when we bought her a few months back. She had a few babies then but I think the other fish ate them all. Call me dumb, but I thought fish laid eggs, I didn't know they gave live birth. She somehow got pregnant again. I didn't even know that the "alleged father" was the same breed of fish! I looked in the tank on Thursday and there were two babies. There was another one on Friday. Then on Saturday I looked in there again and there were a total of 4. How long does it take a fish to give birth to 4 babies???